The present invention relates to a semiconductor laser diode and an optical module on which the semiconductor laser diode is mounted. Examples of the optical module include an optical transmitter, an optical transceiver and so forth.
Conventionally, an InGaAsP-based material which is lattice matched on an InP substrate has been used for a 1.3 μm–1.55 μm-band semiconductor laser diode which is used as a light source in the optical communication. Such semiconductor laser diode has been mounted on an optical transmission module together with a thermoelectric cooler in the prior art. One of the conventional semiconductor laser diodes will be described by way of example. FIG. 13 shows a ridge-waveguide semiconductor laser diode having an electrode structure which extends to a reflection face of a laser cavity. In this example, an n-type InP cladding layer 41, an InGaAsP active layer 42 and a p-type InP cladding layer 5 are deposited on an n-type. InP substrate 1. A p-type InGaAs contact layer 6 is formed on an upper face of the P-InP cladding layer 5 which is formed in the shape of a projection for an emission region. A p-side electrode 8, which is an ohmic electrode, is formed on the p-type InGaAs contact layer 6. In general, the p-side electrode 8 comprises a plurality of conductor layers. A bonding pad 11 is formed on the p-side electrode 8, in a manner extending from the p-side electrode 8. An n-side electrode 10 is provided on a backside of the n-type InP substrate 1.
In turn, an InGaAlAs-based semiconductor laser diode, which operates in a wider temperature range to replace the InGaAsP based ones, is reported by C. E. Zah et al. in “IEEE Journal of Quantum Electronics, Vol. 30, No. 2, P. 511 (1994)”. The InGaAlAs-based semiconductor laser diode does not require the thermoelectric cooler during operation at high temperatures. Since a lower cost is desired for the short range Datacom network, developments in a direct modulation type InGaAlAs-based semiconductor laser diode and an optical transmission module including the laser diode is in progress.
Further, in known structures of a semiconductor laser diode using nitride semiconductor material and a buried heterostructure semiconductor laser diode, an electrode metal layer facet in the vicinity of the reflection face is recessed to avoid troubles in the diode fabrication process. For example, Japanese Patent Laid-open No. 2000-277846 discloses a structure of the semiconductor laser diode using nitride semiconductor material wherein a p-side electrode is formed on a contact portion as being extended to a facet of a cavity and a main p-side electrode having its facet at a portion recessed inward from the cavity facet is formed on the p-side electrode. However, since the substrate does not have cleavage properties, the effect of the structure is nothing but a prevention of peeling of the electrodes due to impact accompanying cleavage which occurs at the time of forming the cavity facets and sagging of the main p-side electrode toward the cavity facet. Japanese Patent Laid-open No. 11-340573 discloses a structure wherein no electrode is provided in the vicinity of a reflection face for the purpose of self-sustained pulsation of the gallium nitride-based laser diode, while Japanese Patent Laid-open No. 10-27939 discloses a similar structure for the purpose of preventing electrodes from peeling off due to impact caused by separation at the time of forming cavity facets of a nitride semiconductor laser diode.
Further, Japanese Patent Laid-open No. 3-206678 discloses the conventional buried heterostructure semiconductor laser diode as shown in FIG. 14; however, an effect achieved by a shape of an electrode on a facet is not defined therein. In FIG. 14, reference numeral 1 denotes an n-type InP substrate, 7 denotes a passivation film, 8 denotes a p-side electrode, 9 denotes a first conductor layer of p-side electrode, 10 denotes an n-side electrode, 41 denotes an n-type InP cladding layer, 42 denotes an InGaAsP active region, 43 denotes a lasing region, 44 denotes a p-type InP cladding layer, 45 denotes a p-type InP buried layer, 46 denotes an i-type InP buried layer, 47 denotes an n-type InP buried layer, 48 denotes a p-type InP buried layer, 49 denotes a p-type InGaAsP buried layer, 50 denotes a mesa channel and 51 denotes a buried mesa.